UK's Cameron says will hunt down 'murderers' of David Haines

British Prime Minister David Cameron said on Saturday the murder of aid worker David Haines by Islamic State was an act of pure evil and vowed to bring his killers to justice however long it takes, Reuters reported.

"This is a despicable and appalling murder of an innocent aid worker. It is an act of pure evil. My heart goes out to the family of David Haines who have shown extraordinary courage and fortitude throughout this ordeal," he said in a statement released by Downing Street.

"We will do everything in our power to hunt down these murderers and ensure they face justice, however long it takes."